1. Field of the Invention.
The present invention relates to syringes and more particularly concerns disposable syringes having non-reusable needle shields.
2. Description of Related Information.
Generally speaking, a hypodermic syringe consists of a cylindrical barrel, most commonly made of plastic or glass, with a distal end containing a hypodermic needle or adapted to be connected to a hypodermic needle and a proximal end adapted to receive the stopper in a plunger rod assembly. The distal end of the barrel or the needle assembly usually includes a needle shield which removably covers the needle to prevent damage to the needle before use and to prevent accidental needle sticks.
At the time of use, the needle shield is removed exposing the sharp point of the needle cannula. Even before use, the sharp point of the needle can inflict minor injury if the user inadvertently sticks himself or herself. After use, the sharpened needle tip poses an additional risk because it may be contaminated and be an instrument for the inadvertent transfer of infection or disease.
Great effort has been expended to minimize the possibility of inadvertent needle sticks. Inadvertent needle sticks can happen during the act of reshielding as the user attempts to guide the sharp needle into the small diameter proximal open end of the needle shield so that the needle shield re-engages the hub or syringe tip. The user may miss the needle shield and stick his or her own hand. It is the belief of some that needle reshielding should not be attempted and the used hypodermic syringe and needle should be disposed of immediately after use in a sharps collecting device. U.S. Pat. No. 4,717,386 teaches a device for uncapping and capping the protective sheath of a hypodermic needle. In one embodiment, a hand-held shield is provided to isolate the fingers from the sheath and to provide a barrier to protect the user in case the needle misses the opening in the sheath upon reassembly. Reshielding devices such as this must be carefully designed and carefully used. The shield material must be strong enough to prevent the needle from penetrating all the way through to the user's hands yet not hard enough so that the needle will slide off the shield into the user's hand. Although this type of device greatly reduces the chance of needle sticks, it does not eliminate it. There are many needle shields in the prior art which are designed with enlarged proximal ends to help shield the user's hand in case the needle is not properly placed back into the cavity of the needle shield. These devices all reduce the risk of accidental needle stick but do not prevent it.
All risk of accidental needle stick caused by reshielding could be eliminated by a syringe having a needle shield structure which, when the needle shield was removed, could not be replaced. There is a need for a simple, straight-forward, reliable, easily fabricated device syringe having a needle shield which cannot be reinstalled over the needle after its removal.